The present invention relates to a so-called crimp and cleave type optical connector ferrule for positioning and securing an optical fiber such that the optical fiber is joined with a mating optical fiber.
FIG. 1 shows a known bonding type optical connector ferrule 20 in which an optical fiber 10 is positioned and secured. In FIG. 1, an optical cord 12, a coated optical fiber 12 and the optical fiber 10 are, respectively, disposed at predetermined positions in a through-hole formed in the known ferrule 20 and are secured by organic adhesive 23. At this time, the optical fiber 10 is secured in the through-hole of the known ferrule 20 by the organic adhesive 23 such that a distal end portion of the optical fiber 10 projects out of an end face of an insert portion 21 of the known ferrule 20. Thus, by polishing the end face of the insert portion 21, a mirrorlike joint end face of the optical fiber 10 is obtained.
The known ferrule 20 has such drawbacks that since the optical fiber 10 is secured by using the organic adhesive 23, a long time is required for injection and curing of the organic adhesive 23, an operator is required to have great skill in polishing the end face of the insert portion 21 and working efficiency is low.
Recently in order to improve working efficiency of mounting the optical connector on the optical fiber, a so-called crimp type optical connector ferrule is proposed in which the organic adhesive is not required for securing the optical fiber. Thus, use of the crimp type optical connector ferrule is spreading in optical communications of factory automation and office automation.
A so-called cleave type optical connector ferrule in which polishing is not required for performing mirror finish of the end face of the optical fiber is developed as another means for improving working efficiency of mounting the optical connector on the optical fiber. Combined with this cleave type optical connector ferrule, the crimp type optical connector ferrule is commercially available and put to practical use as a crimp and cleave type optical connector ferrule. The crimp and cleave type optical connector ferrule greatly improves low working efficiency of mounting the optical connector on the optical fiber, which has conventionally constituted an obstacle to widespread use of optical communication systems, and thus, immensely contributes to widespread use of the optical communication systems.
FIG. 2 shows a prior art crimp and cleave type optical connector ferrule 30 into which the optical fiber 10 is inserted. In FIG. 2, the optical cord 12, the coated optical fiber 11 and the optical fiber 10 are disposed at predetermined positions in a through-hole formed in the known ferrule 30, respectively. At this time, the optical fiber 10 is fitted through a compression sleeve 33. By crimping a portion of a ferrule body corresponding, in location, to the compression sleeve 33 from outside of the ferrule body, the compression sleeve 33 and the optical fiber 10 are secured in the prior art ferrule 30. Meanwhile, the optical fiber 10 is secured in the through-hole of the prior art ferrule 30 such that the distal end portion of the optical fiber 10 projects out of an end face of an insert portion 31 of the prior art ferrule 30. When the optical fiber 10 projecting out of the end face of the insert portion 31 is cut off along the end face of the insert portion 31 with a cutting blade, a mirrorlike joint end face of the optical fiber 10 is obtained.
Cutting of the optical fiber 10 is performed as follows. Initially, a cutting blade 34 is applied to an outer periphery of the optical fiber 10 as shown in FIG. 3aand is slid back and forth so as to produce an initial flaw on the optical fiber 10. Then, a tensile stress or a bending stress is applied to the optical fiber 10 so as to cut off the optical fiber 10.
In the above mentioned prior art crimp and cleave type optical connector ferrule 30, the optical fiber 10 or the coated optical fiber 11 is secured in the prior art ferrule 30 by crimping the ferrule body. However, when the prior art ferrule 30 is subjected to thermal impulse or is allowed to stand under high temperatures, coating material of the optical cord 12 is elongated or shrunk. As a result, a thermal stress is generated in the optical fiber 10. Nevertheless, in order to completely prevent any displacement of the end face of the optical fiber from the original position, the crimping force is required to be increased. However, in this case, such undesirable phenomena are unavoidable that life of the crimped portion of the optical fiber 10 up to its fracture decreases due to a local stress caused by crimping and local transmission loss is increased due to crimping.
Therefore, crimping strength is generally determined in view of displacement of the optical fiber from the original position with time, increase of transmission loss due to crimping, life of the crimped portion of the optical fiber up to its fracture. Hence, crimping strength is not necessarily so determined as to set displacement of the optical fiber from the original position with time at zero and thus, the optical fiber is projected or retracted from the joint end face of the ferrule through, for example, 5 to 15 .mu.m with lapse of time.
Meanwhile, in the case where the optical fiber 10 is cut off by producing the minute initial flaw on the outer periphery of the optical fiber 10 along the end face of the insert portion 31, the mirror surface of the optical fiber 10 may be formed with a burr 10a as shown in FIG. 3b.
Therefore, in the above mentioned prior art crimp and cleave type optical connector ferrule, when the opposed optical connector ferrules are coupled with each other or detached from each other through a connector adaptor or the optical connector is coupled with or detached from an O/E or E/O element receptacle, the burrs of the opposed optical fibers collide with each other or the mirror surface of the optical fiber is damaged through its contact with the burr of the mating optical fiber, thereby resulting in extreme deterioration of performance and quality of the optical ferrule connector. Especially, such an inconvenience as described above becomes conspicuous in the optical connector of a type in which an optical reference surface is disposed at the end face of the ferrule such that the ferrule is positioned in the direction of insertion of the ferrule through contact of the end face of the ferrule with that of the mating ferrule.